Apparatus for offshore recovery and storage of oil and the like



Feb. 28, 1961 M. P. MOLEAN ETA]. 2,973,046

APPARATUS FOR OFFSHORE RECOVERY AND STORAGE OF OIL AND THE LIKE Filed Feb. 7, 1957 e Sheets-Sheet 1 INVENTORS R04: (4 BY Q4. (d 413i,

ATTOR N EY Feb. 28, 1961 M. P. MCLEAN ET AL 2,973,046

\ APPARATUS FOR OFFSHORE RECOVERY AND STORAGE OF OIL AND THE LIKE 6 Sheets-Sheet 2 Filed Feb. 7. 1957 NVENTORS Illllll' ATTORNEY Feb. 28, 1961 M. P. McLEAN ETAL 2,973,046

APPARATUS FOR OFFSHORE RECOVERY AND STORAGE OF OIL AND THE LIKE Filed Feb. 7, 1957 6 Sheets-Sheet 3 so I W'OD-D. I INVENTORJ G" 71 02. 7mm

QM M3 4 64 I BY 62M /4 1110A ATTORNEY Feb. 28,' 1961 M. P. MOLEAN ETAL 2,973,046

APPARATUS FOR OFFSHORE RECOVERY AND STORAGE OF OIL AND THE LIKE 6 Sheets-Sheet 4 Filed Feb. 7, 1957 INVENTORS ATTORNEY Feb. 28, 1961 M. P. MCLEAN ET AL 2,973,046 APPARATUS FOR OFFSHORE RECOVERY AND STORAGE OF OIL AND THE LIKE Filed Feb. 7, 1957 6 Sheets-Sheet 5 R n N BY MN- ATTORNEY Q' N INVENTORS Feb. 28, 1961 M. P. MCLEAN ET AL 2,973,046

APPARATUS FOR OFFSHORE RECOVERY AND STORAGE OF OIL. AND THE LIKE Filed Feb. 7, 1957 6 Sheets-Sheet 6 BY @wemk MR ZMW ATTO R N EY APPARATUS FOR OFFSHQRE RECOVERY AND STORAGE OF OIL AND THE LIKE Malcom P. McLean, Mobile, Ala., and Robert H. Macy, Paseagoula, Miss, assignors to McLean Industries Inc., Mobile, Ala., a corporation of Delaware Filed Feb. 7, 1957, Ser. No. 638,771

Claims. (Cl. 175-8) The present invention relates to offshore recovery of fluid minerals, particularly liquids such as petroleum, and its principal objects are to provide new and improved apparatus and methods for drilling subaqueous wells, recovering fluid deposits therefrom, and handling the recovered fluids through operations including storage on the site of recovery whenever necessary for improved economy and efficiency in movement to ultimate destination.

More particularly the invention provides mobile oil well drilling apparatus for marine use capable of being readily and relatively inexpensively floated and moved to a desired location and there lowered to stable rest on the floor or bottom of the body of water for prospecting and/or drilling and pumping operations throughout any desired period of time, followed by withdrawal of the customarily removable drilling and well structure and flotation and movement of the apparatus to a new location.

Another object is to provide submerged on-the-site storage for recovered liquids, such as oil, so as to eiiect economies in reduction of the standby time of tankers calling to remove the same.

A related object is to provide a novel relationship of ballast and storage tank means in apparatus of the type indicated so that the equipment may be initially lowered by admission of ballast such as water and may thereafter be maintained in lowered position by replacement of the ballast by recovered liquid, suc-h'as oil, kept in storage in the tank means.

A further object is to effect economies in the provision of equipment of the type indicated by utilizing pre-built hulls, such as particularly the bulls of Liberty ships which may at relatively low cost be suitably converted to serve as the flotation and submerging elements or" the apparatus.

General objects are concerned with increasing the stability of the mobile equipment when submerged so that the elevated deck will be maintained entirely motionless, notwithstanding heavy seas, tidal and current movements, wind and the like, with the result that connections between the deck and the subaqueous and subterranean deposits, such as well drilling means, well casings and pumping means, will be maintained as intact and operative as if they were mounted on permanently installed equipment secured to fixed foundations.

Incidental objects are concerned with increasing the flexibility of the equipment, as by mounting the drilling and pumping apparatus for limited movement on the deck of the structure so that a plurality of wells may be successively drilled and exhausted while the structure remains fixed in lowered position, without requiring flotation and removal, and by arranging the structure as a whole for limited bodily movement without requiring full surfacing of the submerged portions, and with generally simplifying the construction, reducing manufacturing and operating costs, and enhancing the efficiency of operation of equipment of the type indicated.

Other objects and advantages will be evident to those States ate skilled in the art from a consideration of the presently preferred embodiments of the invention, which are illustrated in the accompanying drawings, in which- Figure l is a side elevational view of a complete embodiment of the invention shown in lowered, operative position, with the supporting hull structures submerged and resting on the floor of a body of water;

Fig. 2 is a similar View, on a relatively reduced scale, showing the structure afloat but anchored in position for lowering;

Fig. 3 is a bow and elevational View of the structure shown in Fig. 2;

Fig. 4 is a side elevational view of the structure shown in Fig. 2 lowered in operative position;

Fig. 5 is a bow end elevational view, like that of Fig. 3, but showing the structure lowered in operative position;

Fig. 6 is a bow end elevational view, on an enlarged scale, of the structure shown in Fig. 5, again shown in lowered operative position;

Fig. 7 is a detail sectional view through a bilge of one of the hulls, shown on an enlarged scale;

Fig. 8 is a horizontal sectional view, showing the hull top decks in plan, taken on the line 88of Fig. 1;

Fig. 9 is a vertical sectional view taken on the line 99 of Fig. 8;

Fig. 10 is a top plan View of the platform deck;

Fig. 11 is a detail vertical sectional view taken on the line 1111 of Fig. 10;

Fig. 12 is a detail vertical sectional view of a modification;

Fig. 13 is a bow end elevational view of a further modified form of construction; and

Fig. 14 is a horizontal sectional view taken on the line 1414 of Fig. 13.

For clarity of illustration certain details of construction have been omitted from some of the figures, as will be evident from a comparison of Figs. 1 and 4, for example.

It is to be understood that these figures, and the following description of them, are given merely by way of exemplification of the inventive principles and not by way of limitation to the particular structural parts, features or method steps peculiar to them, since it is not necessary that all such parts, features or steps be used conjointly or in the particular form here disclosed except as required by the broader of the appended claims which define the scope and purview of the invention.

As shown in the drawings, and referring first to the form of the invention depicted in Figs. 1-11, the invention comprises essentially a pair of separate hulls, rigidly secured together in laterally spaced parallelism and supporting a plurality of columns which in turn support an elevated platform deck on which is mounted appropriate equipment for drilling, pumping, and otherwise operating in connection with the recovery, of subaqueous liquid deposits such as offshore petroleum, with tank means provided in the hulls and/or in the columns for alternatively buoying thestructure into floating condition for movement to a new location or sinking it so that the bulls rest fixedly on the bottom of the body of water, and preferably also with provision for storing recovered petroleum or the like in saidtank means.

In these drawings, the reference numeral 1 designates generally each one of a pair of bulls which, preferably for considerations of convenience, etficiency and economy, may be the modified or converted hulls of Liberty ships the dimensions of which (stated here, like all dimensions and proportions purely to exemplify a particular opera tive embodiment of the invention and with no intention of limitation) are approximately 441 feet in length, 56 feet in beam, and 37 feet in depth from deck to keel. These hulls converted as hereinafter explained, are rigbeaming generally designated 2, including directly transverse girders 3 and diagonals 4 in sufficient number and of adequate depth and strength to join the hulls, at a suggested spacing of some 90 feet, into a rigid assembly.

The hull assembly supports an elevated, generally rectangular platform deck 5, whose dimensions in the embodiment now being described may be some 310 feet in length and 190 feet in width fixed at a height of approximately 150 feet above the plane of the bottoms of the hulls. The support is provided by means of a plurality of column members including, in the present example, four main columns 6 and a larger number of supplemental or auxiliary columns 7 upstanding from each hull.

The platform deck comprises a rigid slab made entirely or principally of metallic beam joist members and suitable flooring elements, in general like the deck of a merchant ship, so that it is extremely rigid and strong, and thus it cooperates with the cross beaming 2, and with diagonal braces 8 (see Figs. 3 and to join the hulls and deck into a remarkably rigid assembly. This we regard as an important feature of the invention.

The main columns 6 are of special construction which will now be described. Each of them is made of heavy gauge steel plate and is hollow, open at the bottom, and internally braced as best shown in Fig. 8.' Each column is of stepped construction, comprising preferably three superposed cylindrical sections of decreasing diameter from bottom to top. In the illustrated embodiment of he invention the lowermost section 19 is 24 feet in outside diameter, the intermediate section 11 is feet, and the uppermost section 12 is 8 feet. The axial length of the columns is such as to mount the platform deck 5 about 150 feet above the plane of the hull bottoms, as has been stated hereinabove.

Each of the columns 6 is based on a non-watertight second deck 14 of stout, heavily braced and strongly supported construction, below the top deck .15, which is watertight. These may be the original first and second decks of the-Liberty ships, suitably converted as by removing all superstructure from the first deck, closing all batches and other openings therein, reinforcing the second deck, etc. The second deck 14 supports also the auxiliary columns 7, which are of 6 feet outside diameter, and the diagonal supports 8, which are of 4 feet outside diameter may be mounted on the girders 3, as shown in Figs. 6 and 8.

As best shown in Fig. 9, the bulls are strengthened, rigidified and Weighted by concrete fills 17 in the double bottoms and 18 and 19 in the stern and bow compartments respectively. As is also shown in this figure, each hull is subdivided by watertight bulkheads 20 into a plu rality of tanks 22. These tanks are watertight, each of them being defined by the hull bottom, the watertight top deck 15, and a pair of watertight bulkheads 26 extending the full height of the top deck above the bottom. These tanks, in combination with the hollow columns 6 which are in communication with them, constitute the tank means or reservoirs for holding alternatively ballast or stored liquid minerals (hereinafter called oil because petroleum is the principal liquid with which it is proposed to use the invention) and for containing air in displacement of the ballast or oil when the apparatus is to be floated.

The ballast that is used is water taken from the body of water surrounding the apparatus. Because most operations contempltaed for the apparatus will be conducted over the Continental Shelf, off the ocean or gulf coasts of the United States, the ballast will in most cases be sea water and may be so designated in this description. The sea water and oil are supplied to and pumped from the tank means by equipment that will be explained hereinafter following a, description of the platform, deck apparatus,

On the platform deck are built a number of housing structures appropriate for the conduct of oil well drilling and pumping operations and for accommodating a full complement of operating personnel. Such buildings may comprise crew quarters such as a bunk house and mess ball, as well as a generator room, mud pump room, dry mud house, machine shop, tool shack, etc., etc., all of which are represented on the drawings by the several buiidings designated 25.

Also on the platform deck are mounted well drilling apparatus and appurtenances such as a mast, derrick, draw works, pipe racks, etc., most of which are of conveutional construction and hence require no specific description. However, some of the details of the arrangement for mounting the drilling equipment, and particularly the means for rendering it sufficiently flexible and adaptable to movement through a range of locations for drilling different wells without moving the apparatus as a whole, are novel and important and accordingly will now be described.

A derrick 30 is mounted on the platform deck, preferably one at each end of the deck so that wells may be drilled and oil pumped therefrom at locations spaced apart longitudinally of the structure by distances of the order of 300 feet or more without moving the structure. The derrick assemblies are identical, so that a description of one of them will sulfice for both. Each comprises a mast member 31 which is best arranged for retraction to a shipped or downfolded position shown in broken lines in Fig. 1 by hinging its bottom to a base 32 and providing a telescopic brace structure 33 aifording support for the elevated position.

The base 32 includes a bed 34 which is mounted on a substructure 35 in the form of a carriage that is movable transversely of the deck on ways 37, as by flanged wheels journaled on the carriage and engaged with rails extending across the deck. The base bed is skid mounted on the carriage so as to be capable of fore and aft movement through some 10 feet, more or less, across a transverse opening 38 in the deck, by actuation of a hydraulic jack 40 that is movable along a guide rail 4 as the substructure 35 moves along'the ways 37, as by pull cables 42 operated by winches 43. The range of movement of the derrick across the deck is thus limited only by the length of the ways 37, and it is possible to arrange the structure for positioning the derrick at sub stantially any location across the whole width of the deck. Of course vertical drilling is not possible when the derrick is positioned directly over one of the hulls 1, but it has been found that with a lateral travel of 164 feet, which has been incorporated in the specific embodiment of the invention that is the subject of the present description, it is possible for each derrick rig to drill through the opening 38 about 22 holes at an eight foot spacing, with an additional 21 holes drilled by retracting the substructure, for a total of about 86 wells for the two derricks without moving the structure as awhole to a new location.

The specific drilling, casing and pumping means, draw works, and most of the other equipment and apparatus can all be conventional and need not be described, either in respect of structure or mode of operation. However. the invention includes certain novel structure and process operations relating to the handling of oil pumped from the wells, and these will be described. First, however, it seems appropriate to explain the ballasting and related equipment and operation by which the structure is submerged to well drilling position.

With all of the tank means, or enough of them, suffciently empty to provide adequate buoyancy, the struc ture floats and can be towed to a desired location. The tanks are then flooded sufficiently to cause the hulls to sink below the water surface 49 until they rest on the bottom 50 of the body of, water, e.g., the ocean fioor. Flooding is. accomplishedbya novel arrangement of deck The system includes a plurality of water supply pipes 52 positioned between the hulls 1, with their intake ends 53 well below the light waterline of the hulls and well above the bottoms thereof, containing deep well type pumps operated by motors 54 on the platform deck 5. A line of deep well type pumps that are entirely adequate and satisfactory for this use is manufactured and sold by Byron Jackson (30., of Los Angeles 54, California. The structure and principles of operation of these pumps are well known, being shown in such patents, for example, as No. 986,827, issued March 14, 1911, to Franklin H. Jackson, No. 1,149,633, issued August 10, 1915, to Matthew T. Chapman et al., and No. 1,301,597, issued April 22, 1919, to Albert C. Paulsmeier. The arrangement is such that water can be pumped up the water supply pipes 52 from their inlets 53 between the hulls 1 by the deep well type pumps in the pipes operated by the motors 54 and distributed by deck piping 55 through valves 56 to water delivery pipes 57 extending down substantially the full length of certain of the auxiliary columns 7, a pipe 57 being provided in at least one of the columns 7 communicating with each of the tanks 22. An acceptable arrangement will be clear from a comparison of Figs. 8 and 9, considered with Fig. 10, from which it will be evident that sea water, for example, may be delivered selectively to the lower zone of any of the tanks 22 by proper operation of the motors 54 and valves 56. With the tanks 22 sufliciently flooded, the hulls sink and come to rest on the bottom 50 of the body of water, settling with more or less pressure depending on the total weight of the ballasted apparatus.

In this connection it may be mentioned that additional assurance of stable positioning of the structure on the bottom may be provided by equipping the hulls with scour coamings 6i) outwardly and downwardly directed from the bilges, and additionally by anchors 61 on lines 62 controlled by winches 63 at the four corners of the platform deck 5. As best shown in Fig. 7, the scour coaming may be made of heavy plate reinforced by gussets 64 and welded to the hull plate.

As best shown in Fig. 11, water ballast is pumped out of the tanks 22 through exhaust pipes 65 extending down into each of the tanks to substantially the bottom thereof and rising through the various columns 6 to the platform deck 5. A convenient arrangement for the upper ends of the pipes 65 in connection with one of the columns 6 is shown in Fig. 11. In each case, as there shown, the upper end portion of the pipe 65 contains a deep well type pump which is driven by a motor 66 on the deck. A short distance below the deck the pipe 65 is provided with a branch 67 controlled by a valve 68 operated by an actuating rod 69 so that the position of the valve 68 will determine whether the liquid contents of the tank 22 at the bottom of the column will be discharged through the branch 67 and thus dumped or will be lifted to the deck and discharged through the short horizontal outlet pipe 7% which is mounted on the deck. As will be explained hereinafter, ballast water will be dumped through the branch 67 when the tanks are to be emptied and the submerged apparatus is to be re floated, or when the ballasted tanks are to be emptied of their water to make room for oil to be stored. Alternatively, the pump can be operated to lift oil and discharge it through the branch 74 when the tank 22 is full of oil and is to be emptied in order to float the apparatus, in which case the stored. oil will be delivered, as to a tanker whose holds can be supplied by flexible conduits connected by suitable couplings to the ends of the branches 70 of the several pipes 65.

As is best shown in Fig. 11, the uppermost end of each of the columns 6, comprising the smallest diameter section 12 thereof, affords strong structural support for the platform deck and communication through the 8 deck is provided by a short pipe 71, amounting virtuall to a nipple just long enough to extend down through the deck, where it terminates in a wide open end, inside the column 6. Each of these pipes 71 is valved at 72 on the deck and is there elbowed into a horizontal nipple 73 which may be of the same diameter as the outlets 70. Like the outlets 70, the nipples 73 are at times used to deliver oil, and to that end they are, like the outlets 7t), terminally threaded or equipped with unions or other means for coupling hoses or equivalent flexible conduits for conveying oil to the hold of a tanker, to a shore pipeline, or for other disposition as may be desired. At other times the nipples 73 will be coupled to the delivery conduits from the oil well pumps, so that oil being recovered from the wells will be discharged through the pipes 71. into the upper ends of the columns 6 and thence into the tanks 22, to fill those tanks from the bottom or to be added in floating relation to any water that may be in them.

In operation the apparatus is floated by the buoyancy of its empty tanks and columns and is towed to a location where a submarine well can be drilled by the equipment carried by the rig at either end of the platform deck when set at any position along the ways 37. Thus located, the hulls are submerged by operating the pump motors 54 to draw sea water up the supply pipes 52 and discharge it through the delivery pipes 57 into the bottoms of the tanks 22 so as to flood as many of the tanks as may be desired or required. At this point it is worth'noting that it is recommended that all the tanks 22 be ballasted to capacity when the structure is fully submerged, thus minimizing the hydrostatic head differential. In actual practice those tanks which are first to be flooded become full at about the time the hulls are awash and the head in these tanks is equalized. Consequently very little reinforcement is required in these tanksthe tanks which are first to be flooded. The tanks that are flooded after the hulls are submerged require good reinforcement, the details of which are not shown in the drawings but which can be easily provided in the form of struts, gussets, concrete lining, etc., as will be understood.

With the hulls submerged and the scour coamings 60 embedded in the bottom 50, the anchors 61 may be employed further to fix and hold the position of the apparatus. Either or both of the rigs may then be operated in the usual manner, after setting the carriage substructure 35 and/or bed 34 of its base in desired position along the ways 37 and with appropriate fore and aft adjustment. Drilling and subsequent pumping operations are conducted in the customary way as is well offshore structures. However, in the preferred method or process practiced in the use of the present invention,

the lines delivering oil recovered from the wells are connected to the nipples 73 (Figs. 10 and 11) so that the oil is pumped through the pipes 71- into the tanks 22 for storage, displacing the water ballast therein, which is simultaneously removed through the pipes 65, 67, and functioning itself as ballast, being kept in the tanks and columns until it becomes convenient to remove it, as by pumping it into the holds of a tanker. This oil storage feature of the invention we regard as important because it greatly reduces the tanker standby time from that which is required when storage is not provided and the oil must be pumped directly from the well to the tanker. With the new method, the oil is stored as rapidly or as slowly as it is recovered from the wells, without requiring any tanker to be present. Then, when the tanks contain enough oil to fill a tanker, no more than a very short period of time is necessary to force oil simultaneously through several or all of the discharge nipples 73 and the flexible conduits coupled thereto for delivery into the tanker holds.

At the same time that oil is thus being delivered from aevaoae a. tank, water ballast of equal volume and of slightly greater weight will be supplied to the same tank by the pipe 57, thus maintaining approximately constant the total weight of the apparatus and its stability on the bottom 50. An important feature of the invention, considered as a process or method, is the step of replacing oil pumped from storage with water taken in as ballast, particularly replacement in the same tank or tank means (the tank proper and the communicating column 6 and/or 7, considered as a unitary reservoir), because in this way a submerged tank means may be kept at all times filled with liquid (oil or water or oil and water), thus maintaining the hydrostatic head substantially constant and minimizing the need for heavy reinforcement, bracing, concrete lining and the like. We regard this as an especially advantageous feature of the invention.

It will be understood that when all the wells within the range of movement of the two rigs have been drilled and all the oil pumped therefrom into the tanks and thence discharged to tankers or otherwise, the apparatus may be floated by emptying the tanks 22 or sufhcient of them to buoy the hulls until they are awash or otherwise in floating condition, whereupon the apparatus may be towed any distance to a new location for repetition of the operation. The tanks that are first emptied in this re-fioating operation should be made structurally strong by more liberal application of bracing, concrete lining, etc., than'is required of the tanks that can be kept continuously flooded, as has been explained.

If movement of the re-floated apparatus through some relatively short distance only is desired, for drilling a new Well pattern just a few feet from the first one, it will be found sufficient to pump out just enough ballast to raise the hulls a few feet off the bottom, followed by shifting by means of the anchor winches 63. For this purpose the anchor lines 62 may be passed through sheaves 75 mounted on the bow and stern of each of the hulls 1 so that the anchors 61 may be heaved lat ,erally some distance with the aid of deck booms (not shown), or even aft or forward, and a pull having a strong horizontal component effected by operating the winches 63 to move theapparatus in the desired direction through the water. This arrangement of the anchor lines is shown in Figs. 1 and 6. In Figs. 2 and 3 the lines are shown free of the sheaves, being there used simply to augment the hold of the apparatus on the bottom 59. This limited mobility of the apparatus without fully floating it renders it unnecessary to mount more than two drilling rigs on the platform since the rig at one or the other end can be positioned by proper manipulation of the anchor winches to cause turning of the apparatus, over a location that would underlie any rig that might have been positioned on either of the sides of the platform deck. Certain other features of the apparatus and method comprising the invention are regarded as noteworthy and will now be briefly discussed.

Designing the columns 6 in the form of hollow sections of different diameters, with the section of greatest diameter at the bottom and that of smallest diameter at the top, increases the storage capacity of the tanks 22 because oil can be pumped into the tanks to fill them and then can be continued to be supplied until the columns also are full. The stepped character of the columns not only increases the capacity of the lower portion of each column over that of a column of uniform Smaller diameter, but it appreciably reduces the wave resistance, i.e,, the surface area of the columns exposed to wave action, which of course is greatest near the water surface. Contributing also to the resulting increase in stability is the lowering of the center of gravity by concentrating the major portion of the weight of the columns in their lower portions.

Moreover, large diameter columns, representing in toto a quiteappreciable portion of the displacement of the entire apparatus, constitute a natural hydrostatic brake to prevent an excesively rapid rate of ascent in cases when, in the operation of raising the apparatus by emptying the tanks, the hulls suddenly break loose from a stuck condition in a muddy bottom. In such upward movement the displacement diminishes rapidly because of the large column diameters that rise from the water, so that weight and displacement quickly become equal and ascent ceases.

The stabilizing effect of large diameter columns on spacedhulls, i.e., hulls located remote from the centerline, is greater than that of small diameter columns for the following reason also:

The principal criterion of stability, once the bulls become awash, is the moment of inertia of the columns, which is measured almost entirely by the cross-sectional areaof the columns multiplied by the square of the distance to the centerline. Since the cross-sectional area of the columns increases with the square of the diameter, and the moment of inertia increases with the square of the distance to the centerline, it follows that a very high degree of stability is achieved by large diameter columns set back far from the centerline. Hence the advantage of the twin, spaced hull construction with its large diameter, widely spaced columns.

Stability of the rig, as measured by metacentric height, in a typical embodiment of the present invention for various degrees of submergence, i.e., draft, is as follows:

Condition Metacentrlc Height, feet Draft, feet While of course specific-dimensions constitute no part of the inventive concepts, and proportions and relative values maybe altered considerably without departing from the inventive principles, it may be pointed out that a structure of the size herein suggested has a total combined tank and column (designated tank means in the claims) capacity of 259,900 barrels of oil and imposes a load on the-bottom 50 of the body of water of approximately 315 pounds per square foot, which is well below the generally accepted safe limits.

In this connection, a slight modification of the preferred construction hereinabove described may be adopted as added insurance against undue settling in soft mud or lateral shifting. In this modification, as shown in Fig. 12, four of the eight end columns 76, corresponding to the small diameter columns 7 of Figs. 1-10, are extended through the tanks 22, to the bottoms of the hulls, and are open through the bottoms and are provided with retractible and projectible s uds 7'7, connected by extensions '73 comprising operating rods projected through the platform deck 5 for driving and withdrawal by any suitable power means. When driven into otherwise troublesome bottoms such spuds are effective so as considerably to increase fixation of the structure against undesired movement.

A further modification is shown by Figs. 13 and 14, in which the girder and diagonal type of cross beaming 2 of Figs. ll1 is replaced by a pair of longitudinally spaced auxiliary tanks Sit. These may be fabricated from steel plate, with suitable internal bracing and appropriate connections to the two hulls, to provide all the rigidity of the beaming 2 and in addition increase the storage capacity of the tank means. They may be connected to the deck platform by supply and discharge pipes, or they may be made communicating with one or another of the tanks 22, to be filled and discharged with such tanks,

and they may be used for any of the purposes for which the tanks 22, column ,6, etc., are used, i.e., for ballast, recovered oil storage, or as reservoirs for operating liquid supplies, such as fuel oil, fresh water, etc. The construction employed in the Figs. 13 and 14 embodiment of the invention is otherwise the same as that of Figs. 1-11, including if desired the spud modification of Fig. 12.

While the apparatus has been explained in terms of its application to the drilling of oil wells and the recovery of petroleum from submarine deposits, it is believed to be obvious that the invention is capable of being employed, without substantial or inventive modification, in the recovery of other mineral fluids, and particularly liquids, from other underwater deposits. Among these may be mentioned, without limitation, liquefied sulfur, brine, asphaltic hydrocarbons, and gas. The essential components of the combinations comprising the apparatus and the method of using it are not determined by the material recovered but are defined by the broader of the appended claims, in which, in the interest of brevity, the term oil is used as a generic designation of all and any recoverable liquids on which the apparatus is capable of being used.

We claim:

1. Apparatus for offshore drilling and recovery of oil comprising a pair of separate hulls each having tank means for containing alternatively water ballast and oil in storage including tanks within the hull and a plurality of columns mounted on the hull and communicating with the tanks, rigid connecting means securing said hulls in fixed laterally spaced relation, a platform sup ported on said columns spanning the plan projection of said pair of hulls and surmounting all of said columns and cooperating with said rigid connecting means to integrate said apparatus into a rigid assembly, drilling and pumping equipment mounted on said platform for recovering oil from beneath a body of water surrounding the apparatus and raising the same to said platform, means for supplying selectively water ballast and said oil to each of said tanks including piping and additional pumping equipment, said piping and additional pumping equipment for each of said tanks comprising a water elevating pipe positioned outside the hulls, a deep Well type pump in said water elevating pipe, a water delivery pipe connected to said elevating pipe and extending down into the bottom of said tank for discharging water into said tank to flood said tank means and sink said hulls, and other pipes extending from the platform into said columns including a relatively short oil pipe extending into the upper portion only of each of said columns for supplying oil thereto and discharging therefrom oil displaced by water from the water delivery pipe, and including also a relatively long pipe projecting down to substantially 10 the bottom of the tank and containing a deep well type pump for withdrawing alternatively water or oil from the tank so as fully or partially to empty the tank and float the apparatus.

2. Apparatus as claimed in claim 1 in which the columns into which the relatively short oil pipes and the relatively long pipe for withdrawing alternatively water or oil extend are substantially circular in cross section and are formed of a plurality of superposed concentric sections of different diameters, the lower sections being of greater diameter than the upper sections, and the sections being axially fixed together.

3. Apparatus as claimed in claim 1 in which each of the columns into which the relatively short oil pipes and the relatively long pipe for withdrawing alternatively water or oil extend is formed of three cylindrical sections axially superposed in fixed relation on one another, comprising a lowest section of greatest diameter, an uppermost section of smallest diameter, and an intermediate section of intermediate diameter.

4. Apparatus for offshore drilling and recovery of oil comprising a pair of separate hulls each having tank means for water ballast and oil storage including tanks Within the hull and a plurality of hollow columns mounted on the hull and communicating with the tanks, a rigid connection securing said hulls in fixed laterally spaced relation, a platform supported on said columns, drilling and pumping equipment mounted on said platform, each of said columns comprising a plurality of superposed concentric sections circular in cross section and of different diameters, the lower sections being of greater diameter than the upper sections and the sections of each column being axially fixed together, and means for flooding said tank means, including said tanks and columns, progressively by filling first the tanks and thereafter the larger and finally the smaller sections of the columns, so as to sink the hulls and columns in a body of water.

5. Apparatus as claimed in claim 4 in which the means for flooding the tank means comprises piping entering the tanks exclusively through the columns.

References Cited in the file of this patent UNITED STATES PATENTS 1,759,644 Reed-Hill May 20, 1930 1,811,761 Roberts June 23, 1931 2,248,051 Armstrong July 18, 1941 2,515,540 Willey et a1. July 18, 1950 2,622,404 Rice Dec. 23, 1952 2,772,539 Sandberg Dec. 4, 1956 2,777,669 Willis et a1. Jan. 15, 1957 

